From the logs it can be seen that the bootloader (MBR) is written to sdb 2017-01-02 20:18:59 <1> mycloud(14014) [Ruby] bootloader/mbr_update.rb:66 Copying generic MBR code to /dev/sdb 2017-01-02 20:18:59 <1> mycloud(14014) [Ruby] lib/cheetah.rb:158 Executing "/bin/dd bs\=440 count\=1 if\=/usr/share/syslinux/mbr.bin of\=/dev/sdb".